I have read/write access to it and can normally manually move files across with no problems.

Symptom: I drag 7 tv show files to it. It quickly finds them all correctly and shows the final confirmation screen, and they're all ok. I try to proceed, and it then quickly goes through all of them and returns the redline error, "Renamed/Moved -7 files. Skipped: 14"

I have "auto move" selected in the config. If I disable this, the app performs the rename/move instantly but doesn't actually do anything, and claims that it was successful.

After investigating this, it turns out my destination drive does not have enough space on it. So the app behaves in very unexpected ways rather than returning a clear indication that the moves failed because of lack of disc space.